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Biomedical subjects

T J Martin

Publications and source records attributed to T J Martin.

At least 19 recordsLinked to original sources
PubMed1992

Abundant expression of parathyroid hormone-related protein in human amnion and its association with labor.

In animal models, parathyroid hormone-related protein (PTHrP) increases placental calcium transport and inhibits contraction of uterine smooth muscle. The present studies were undertaken to characterize the expression of PTHrP in human uteroplacental tissues. PTHrP mRNA was identified by Northern analysis as a single species (approximately 1.8 kilobases) in human amnion, chorion, placenta, decidua, and myometrium. The most abundant signal was seen in amnion, where it was 10-400 times that in the other uteroplacental tissues. PTHrP mRNA abundance was decreased in amnion (but not in the other tissues) following the onset of labor (P less than 0.001). PTHrP mRNA in amnion appeared to be translated to a bioactive peptide, as PTHrP bioactivity and immunoreactive PTHrP in amnion correlated closely with PTHrP mRNA content (r = 0.86 and 0.95, respectively; P less than 0.05 and P less than 0.01). Amniotic fluid contained PTHrP, 21 +/- 6 pmol/liter (n = 10) at 16 weeks and 41 +/- 9 pmol/liter (n = 7) at 38 weeks (P = 0.05). These concentrations equaled or exceeded those found in plasma of patients with hypercalcemia secondary to PTHrP. After rupture of the fetal membranes, PTHrP mRNA in amnion was decreased by 78% (P less than 0.0001). This decrease appeared to be specific for PTHrP mRNA, as glyceraldehyde-3-phosphate dehydrogenase mRNA was unchanged following rupture of membranes. Like PTHrP mRNA, PTHrP bioactivity and immunoreactive PTHrP in amnion decreased significantly following rupture of membranes (P less than 0.03 and P less than 0.01, respectively). Since PTHrP is a potent antagonist of uterine muscle contraction, the decrease of PTHrP following rupture of the fetal membranes may play a key role in the onset of labor.

Amnion↗
PubMed1992

Leukaemia inhibitory factor and bone cell function.

A bone-resorbing product of mouse spleen cells found to have differentiation-inducing activity was most probably leukaemia inhibitory factor (LIF). This revealed that LIF is a cytokine active on bone, in addition to its several other sites of action. In organ culture of newborn mouse bone, recombinant LIF promoted bone resorption by a prostaglandin-dependent process. Resorption by isolated rat osteoclasts was also promoted by LIF through an initial action on osteoblasts which was receptor-mediated. Incorporation of [3H]thymidine into DNA was increased by LIF in cells (most probably osteoblasts) of the newborn mouse bones. Osteoblasts have been shown to produce LIF, and the amount is increased by treatment with retinoic acid or TNF-alpha. LIF also acts directly on osteoblasts to inhibit plasminogen activator activity, by stimulating the synthesis of plasminogen activator inhibitor 1 mRNA and protein. The latter actions are very similar to those of TGF-beta. Again like TGF-beta, LIF was ineffective in promoting bone resorption in vitro in fetal rat long bones. These results, together with the in vivo data showing that high circulating levels of LIF in the mouse are accompanied by a substantial increase in trabecular bone mass, indicate that LIF is another cytokine with potent actions on bone and potentially important interactions with other osteotrophic factors.

Animals↗
PubMed1992

Localization of parathyroid hormone-related protein mRNA expression in breast cancer and metastatic lesions by in situ hybridization.

Parathyroid hormone-related protein (PTHrP) has been identified immunohistochemically in 60% of breast carcinoma and in 92% of breast cancer metastases in bone. To establish whether the localization of the PTHrP antigen reflects protein synthesis and also to investigate the role of PTHrP in metastatic disease, as part of an ongoing study, we used in situ hybridization to study the localization of PTHrP mRNA in a retrospective series of primary breast tumors and their metastatic lesions. Paraffin sections of 17 primary and 26 metastatic lesions, 11 of which were in bone, were available for the study: 10 of the 17 (59%) primary lesions, 8 of 11 (73%) breast cancer metastases to bone, and 3 of 15 (20%) metastases to non-bone sites showed specific localization of PTHrP mRNA. These findings establish that PTHrP is commonly synthesized by primary breast cancers and support previous immunohistochemical studies reporting a higher incidence of PTHrP-positive tumor cells in skeletal metastases than in nonskeletal metastases.

Breast Neoplasms↗
PubMed1992

Plasminogen activator regulation in osteoblasts: parathyroid hormone inhibition of type-1 plasminogen activator inhibitor and its mRNA.

In order to determine the mechanism by which parathyroid hormone (PTH) stimulates plasminogen activator (PA) activity in rat osteoblasts, we investigated the effect of human PTH(1-34) [hPTH(1-34)] on the synthesis of mRNAs for tissue-type PA (tPA), urokinase-type PA (uPA), and PA inhibitor-1 (PAI-1), and on release of PA activity and PAI-1 protein in both normal rat calvarial osteoblasts and UMR 106-01 osteogenic sarcoma cells. hPTH(1-34) (0.25-25 nM) decreased PAI-1 mRNA and protein, and increased PA activity in both cell types in a dose-dependent manner with ED50 of about 1 nM for both responses. Forskolin and isobutylmethylxanthine also stimulated PA activity and decreased PAI-1 protein and mRNA in both cell types. hPTH(1-34) did not show any consistent effect on tPA and uPA mRNA in calvarial osteoblasts, but a modest (two-fold) increase of both mRNAs was observed in UMR 106-01 cells treated with 25 nM hPTH(1-34). However, when protein synthesis was inhibited with 100 microM cycloheximide, the increase of tPA and uPA mRNA by hPTH(1-34) was enhanced in UMR 106-01 cells and became evident in calvarial osteoblasts. Fibrin autography also revealed that hPTH(1-34) increases tPA and uPA activity, especially after cycloheximide treatment in UMR 106-01 cells. These results strongly suggest that PTH increases PA activity predominantly by decreasing PAI-1 protein production through a cyclic adenosine monophosphate (cAMP)-dependent mechanism in rat osteoblasts. The reduction of PAI-1 protein by PTH results in enhanced action of both tPA and uPA, and would contribute to the specific roles of these PAs in bone.

Animals↗
PubMed1992

Hypercalcemia in cancer.

Hypercalcemia may occur as a complication of haematological malignancies, in association with solid tumors with bone metastases, and with solid tumors in the absence of bone metastases. The latter syndrome, known as the humoral hypercalcemia of malignancy (HHM) shares many features with primary hyperparathyroidism. A parathyroid hormone-related protein (PTHrP) has been identified, isolated and cloned, which is most likely responsible for the calcium disturbances in HHM, PTHrP is a previously unrecognized hormone which has limited amino-terminal sequence homology with PTH and is the product of a separate gene. Tissue localization studies have identified PTHrP in squamous cell carcinomata, renal cortical carcinomata, in a proportion of breast cancers and in adult T-cell leukemia/lymphoma. In normal tissues, PTHrP has been immunohistochemically localized in keratinocytes, placenta and fetal parathyroid glands. In addition to its role in mediating hypercalcemia in cancer, PTHrP is likely to have an important endocrine role in the fetus, and perhaps a paracrine function in several organs.

Animals↗
PubMed1992

Malignant glaucoma after laser iridotomy.

Malignant glaucoma was initially reported as developing after surgery for glaucoma. Subsequently, associations with trauma, inflammation, and the use of miotic agents, as well as spontaneous occurrence have been noted. Laser iridotomy has been assumed to avoid the risk of subsequent malignant glaucoma in eyes with angle-closure glaucoma by avoiding surgical incision of the eye. However, the authors report six cases of malignant glaucoma after laser iridotomy. In all but two cases, medical therapy for the malignant glaucoma resulted in deepening of the anterior chamber and normalization of the intraocular pressure. Malignant glaucoma recurred in five of the patients, and two patients had malignant glaucoma in the fellow eye.

Adult↗
PubMed1992

Parathyroid hormone-related protein: a possible endocrine function in lactation.

OBJECTIVE: Parathyroid hormone-related protein (PTHrP), initially discovered as the factor responsible for the syndrome of humoral hypercalcaemia of malignancy, has also been found to be expressed in placenta, in pregnant uterus, in the fetus at many locations, and in the lactating mammary gland. This study sought to establish whether PTHrP reaches the maternal circulation when it is expressed in mammary tissue during lactation or in the maternal reproductive tract during gestation. DESIGN: Blood samples were collected from 53 subjects: 18 pregnant women in all stages of gestation, 19 lactating mothers and 16 non-lactating post-partum controls. MEASUREMENTS: PTHrP was measured using a specific and validated radioimmunoassay. Parathyroid hormone was measured by two-site immunoradiometric assay. Total calcium was measured by atomic absorption spectrophotometry. RESULTS: Circulating levels of PTHrP were readily detectable in 12 of 19 nursing mothers (range 2.7-7.8 pmol/l) but in none of the mothers who were bottle feeding. PTHrP was also detected in one of 18 pregnant subjects. Parathyroid hormone concentrations were lower in lactating mothers (2.3 +/- 1.0 pmol/l), than in non-lactating mothers (3.5 +/- 1.2 pmol/l) (P < 0.01). CONCLUSION: PTHrP reaches the maternal circulation during lactation in amounts which could produce a systemic effect.

Adult↗
PubMed1992

Production of parathyroid hormone-related protein by the rat mammary gland in pregnancy and lactation.

Production of parathyroid hormone-related protein by the rat mammary gland in pregnancy and lactation. Am. J. Physiol. 263 (Endocrinol. Metab. 26): E1077-E1085, 1992.--Production of parathyroid hormone-related protein (PTHrP) by the mammary gland of Sprague-Dawley rats has been examined using immunohistochemistry and in situ hybridization to detect PTHrP and PTHrP mRNA, respectively. PTHrP and PTHrP mRNA could be demonstrated in nests of epithelial cells of the developing mammary gland at day 14 of pregnancy and in the epithelial secretory cells lining the alveoli during the latter stages of pregnancy and during lactation. A specific radioimmunoassay was also used to measure the concentration of PTHrP secreted in the milk throughout lactation. The concentration of PTHrP in milk was relatively low initially but increased during the latter stages of lactation, whereas calcium concentrations remained virtually constant throughout lactation. No correlation was found between the concentrations of calcium and PTHrP in rat milk. These results show that PTHrP is present in rat milk and also in mammary tissue before parturition, and therefore it may assist in the development of the mammary gland during pregnancy.

Animals↗
PubMed1992

Glucocorticoid regulation of plasminogen activator inhibitor-1 messenger ribonucleic acid and protein in normal and malignant rat osteoblasts.

Glucocorticoids exert potent inhibitory effects on bone formation. We have previously shown that glucocorticoids suppress plasminogen activator (PA) activity in normal and malignant rat osteoblasts. To clarify the mechanism of this suppression, we investigated the effects of dexamethasone on PA inhibitor-1 (PAI-1), tissue-type PA (tPA), and urokinase-type PA (uPA) expression and also on PAI-1 protein and PA activity in both normal rat calvarial osteoblasts and a clonal osteogenic sarcoma cell line, UMR 106-01. Dexamethasone increased PAI-1 mRNA and protein in both cell types. The increase in PAI-1 protein and the decrease in PA activity were obtained over the same concentration range, with a half-maximally effective concentration of dexamethasone of about 10(-9) M. The increase in PAI-1 mRNA caused by dexamethasone was retained with cycloheximide treatment, but abolished with actinomycin-D. Dexamethasone had no effect on tPA or uPA mRNA in either cell type. The glucocorticoid antagonist RU 486 prevented the effects of dexamethasone on PA activity and PAI-1 protein. Dihydrotestosterone, progesterone, and 17 beta-estradiol did not influence PA activity or PAI-1 formation. Although tPA and uPA protein could not be measured, these results suggest that glucocorticoids suppress PA activity predominantly by increasing PAI-1 synthesis in rat osteoblasts. Suppression of PA activity through actions on PAI-1 formation by glucocorticoids could contribute to the mechanisms by which glucocorticoids inhibit bone formation.

Animals↗
PubMed1992

Transforming growth factor-beta modulates receptor binding of calciotropic hormones and G protein-mediated adenylate cyclase responses in osteoblast-like cells.

Transforming growth factor-beta (TGF beta) produced by osteoblasts is present in high levels in bone and influences bone formation, replication of bone cells, and expression of osteoblast protein products. Interactions between bone active hormones and locally released and activated TGF beta were studied by examining the influence of TGF beta preincubation on PTH, calcitonin (CT), and vitamin D receptors in an osteoblastic cell line (UMR 106-06). Preincubation of UMR 106-06 cells with 1 ng/ml TGF beta for 3 days increased specific binding of [125I]PTH-related protein (PTHrP)(1-84) to 140% of that in control cells, but [125I]salmon CT binding decreased to 50% of controls. Binding isotherms indicated that the changes in binding were due to altered receptor numbers since affinities for 125I-labeled PTH and CT remained unchanged. The effect on receptor levels was time dependent, requiring 24 h preincubation with TGF beta for measurable changes, and dose dependent, with maximal effects seen with 1 ng/ml TGF beta. Binding of [3H]1,25(OH)2 vitamin D3 was increased to 130% of control in cytosolic extracts of UMR 106-06 cells pretreated for 3 days with 1 ng/ml TGF beta. Scatchard plots suggested an increase in receptor number without change in affinity. The adenylate cyclase response to PTH increased to 150% of control cells after 3 days of treatment with 1 ng/ml TGF beta; however, the adenylate cyclase response to CT was little changed. Forskolin- and cholera toxin-stimulated adenylate cyclase responses were increased by TGF beta treatment to 130-160% of control, indicating an increase in the stimulatory subunit of the G protein. Increased abundance of both Gs and Gi proteins were indicated by increased cholera toxin- or pertussis toxin-dependent [32P] NAD ribosylation of 47-kilodalton (kDa) and 42-kDa or 40-kDa proteins, respectively, in TGF beta-treated cells. Our data support a complex regulatory effect of TGF beta on UMR 106-06 cells with increases in PTH receptors, vitamin D receptors, and G proteins, whereas there is an apparent down-regulation of CT receptors. TGF beta might induce a more differentiated osteoblast phenotype of these cells, which already express differentiated features such as high alkaline phosphatase activity, PTH and vitamin D receptors, and collagenase production. Since low doses of PTH stimulate bone formation in vivo, TGF beta released or activated at sites of new bone formation might locally modulate PTH activity be allowing increased PTH receptor and postreceptor effectiveness.

Adenylyl Cyclases↗
PubMed1992

Circulating PTH and PTHrP levels before and after treatment of tumor induced hypercalcemia with Pamidronate Disodium (APD).

The effect of lowering ionized calcium on circulating parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) was assessed in twenty patients with hypercalcemia of malignancy following treatment with Pamidronate Disodium. Ionized calcium levels fell rapidly in all treated patients. PTH concentrations were initially suppressed below normal in 18 patients, but rose from 0.48 +/- 0.42 pmol/L to 3.63 +/- 3.13 pmol/L (p less than 0.01) after treatment, reaching higher than normal values in some patients even in the presence of persistent hypercalcemia. PTHrP concentrations did not change significantly after treatment. These findings are consistent with an increased sensitivity of parathyroid tissue to changes in ionized calcium following prolonged exposure to hypercalcemia. Regulation of tumor secretion of PTHrP by calcium was not apparent within the range of calcium concentrations in this study.

Calcium↗
PubMed1992

Retinoic acid stimulates transcriptional activity from the alkaline phosphatase promoter in the immortalized rat calvarial cell line, RCT-1.

The immortalized rat calvarial bone cell line RCT-1 responds to treatment with retinoic acid (RA) by increased expression of osteoblast phenotype-related features, including the induction of liver/bone/kidney alkaline phosphatase (ALP) activity. ALP mRNA could not be demonstrated in unstimulated cells, but was first detected in cells treated for 6 h with 1 microM RA. Cycloheximide failed to block the RA induction of ALP mRNA, indicating that de novo protein synthesis was not a requirement for the RA effect and that the ALP gene may be a direct target for RA action. This was confirmed by nuclear run-on assays, which demonstrated a 2.5-fold increase in the abundance of ALP transcripts after 6 h of RA treatment. To determine whether the RA responsiveness was mediated by a specific segment of the ALP promoter, RCT-1 cells were transfected with a series of plasmids containing deletions of the 5'-flanking sequence of the human ALP gene fused to the chloramphenicol acetyl transferase (CAT) gene. CAT activity was measured in cells cultured in the presence of RA or vehicle. All but the smallest construct, which contained 44 basepairs up-stream of the initiation of transcription, were found to mediate a 2- to 3-fold increase in the expression of CAT activity in response to RA. Furthermore, when the region -108 to -45 of the human ALP gene was inserted into the expression vector pBLcat2, in a position immediately up-stream of the herpes simplex virus thymidine kinase promoter, the construct was found to mediate a 2-fold enhancement of CAT activity in response to RA. In gel retardation assays, a major band was present corresponding to the formation of a complex between the 32P-labeled probe containing the -108 to -45 sequence and proteins present in nuclear extracts of RCT-1 cells stimulated for 3 h with RA. These data suggest that the sequence of 64 basepairs (-108 to -45) 5' to the transcription start site is involved in the RA inducibility of the human ALP gene.

Alkaline Phosphatase↗
PubMed1992

Oestrogen enhancement of the myometrial response to exogenous parathyroid hormone-related protein (PTHrP), and tissue localization of endogenous PTHrP and its mRNA in the virgin rat uterus.

Classical pharmacological studies have shown that oestrogen dominance in humans and other animals can increase the responsiveness of the uterus to many locally acting peptides. Parathyroid hormone-related protein (PTHrP) has been shown to be expressed in the pregnant and non-pregnant rat uterus and exogenous PTHrP is known to relax uterine contraction in vitro. We investigated whether oestrogen dominance can influence the responsiveness of the uterine horn to PTHrP, and further studied the localization of PTHrP mRNA and protein in the rat uterine horn using in-situ hybridization and immunohistochemistry. Exogenous PTHrP(1-34) inhibited spontaneous and electrically induced contractions in uteri isolated from non-cycling rats. Pretreatment of non-cycling rats with oestradiol-17 beta increased uterine sensitivity to PTHrP: EC50 values for inhibition of spontaneous contractions by PTHrP were 0.33 nmol/l, 1.1 nmol/l, 2.6 nmol/l and 7800 nmol/l in uteri from animals treated for 2 days with oestradiol-17 beta alone, 2 days with oestradiol-17 beta + 1 day progesterone, 1 day with oestradiol-17 beta alone and in untreated rats respectively. Similar EC50 values were obtained for electrically stimulated uteri. In agreement with these findings, uterine horns from cycling rats in pro-oestrous and oestrous phases of the cycle showed a higher responsiveness to PTHrP(1-34) when compared with uterine horns taken from rats in metoestrus and dioestrus. PTHrP mRNA and protein were detected in the endometrial epithelium lining of the lumen and the endometrial glands, as well as in the myometrium of rats which were either pretreated for 2 days with oestradiol-17 beta or untreated. This study suggests that PTHrP may act in an autocrine and/or paracrine manner to modulate uterine motility and function.

Animals↗
PubMed1992

An assessment of the ability of human bone marrow cultures to generate osteoclasts.

Several groups have successfully generated osteoclasts in cultures of murine haemopoietic cells. This approach would clearly be useful in the analysis of mechanisms of regulation of human osteoclast formation if analogous results could be obtained in cultures of human bone marrow. This communication describes independent attempts by three groups to generate unequivocally defined osteoclasts from bone marrow obtained from human iliac crest, femoral neck, rib, and from foetuses. The haemopoietic tissue was incubated using techniques described by others for production of osteoclast-like cells, and with variants of this technique using strategies based on our experiences with murine osteoclastogenesis. Haemopoietic cells were incubated with calcium regulating hormones, cytokines, osteoblastic supernatants, and osteoblastic or bone marrow stromal cell layers. Formation of cells capable of excavation of bone slices was rarely seen. Despite the paucity of bone resorbing cells, multinucleate cells (MNCs) developed with similar characteristics to the MNCs that have been interpreted as osteoclast-like in human bone marrow cultures. The MNCs were, however, calcitonin-receptor (CTR) negative, and did not show the typical pattern of reactivity with osteoclast-specific antibodies. They possessed instead an antigenic profile characteristic of macrophage polykaryons. We conclude that the MNCs which consistently generate in human bone marrow cultures do not possess phenotypic characteristics specific for osteoclasts and appear to be macrophage polykaryons. The conditions required for osteoclast generation in cultures of human haemopoietic cells remain to be defined.

Bone Marrow Cells↗
PubMed1991

Specific down-regulation of parathyroid hormone (PTH) receptors and responses to PTH by tumour necrosis factor alpha and retinoic acid in UMR 106-06 osteoblast-like osteosarcoma cells.

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) act via PTH receptors in bone to stimulate bone resorption. Bone resorption is also stimulated by certain cytokines, which are produced in bone and bone marrow. The effects of such cytokines on the PTH-receptor system were studied in the osteoblast-like osteosarcoma cell line UMR 106-06. 125I-labelled PTHrP-(1-84)-peptide bound specifically to the cells, and PTHrP-(1-34) and -(1-84) competed with equimolar affinity for binding to UMR 106-06 cells. The specific binding of 125I-PTHrP-(1-84) could be completely blocked by PTH. Therefore 125I-PTHrP-(1-84) bound to a classical receptor in UMR 106-06 cells. Preincubation for 3 days with either tumour necrosis factor alpha (TNF alpha) or retinoic acid (RA) both decreased the specific binding of 125I-PTHrP-(1-84) to about 40% of control levels. These effects were specific for PTH binding, since there was little effect on 125I-salmon-calcitonin binding. Both TNF alpha and RA required 24 h exposure to cells to produce a measurable effect. The decrease in 125I-PTHrP-(1-84) binding was due to a reduced number of binding sites, with little apparent change in affinity. Half-maximal effects were seen with 1 ng of TNF alpha/ml, whereas 1 microM-RA was needed to observe the loss of PTH receptors. Combinations of RA and TNF alpha produced a greater effect than that of either agonist alone. The loss of PTH receptors was accompanied by a specific loss of PTH-stimulated cyclic AMP production. Preincubation with TNF alpha increased the basal plasminogen activator (PA) activity in the cells and decreased the amplitude of the response of PA activity to PTH compared with control cells. Furthermore TNF alpha decreased sensitivity to PTH (50% stimulation of PA activity with 0.1 nM-PTH in control cells versus 50% stimulation with 0.3 nM-PTH in TNF alpha-treated cells). In contrast, TNF alpha pretreatment increased the amplitude of the response of PA activity to calcitonin, whereas sensitivity to calcitonin was not altered. These data are consistent with a specific down-regulation of PTH receptors in osteoblast-like UMR 106-06 cells after exposure to TNF alpha or RA. The loss of PTH receptors is accompanied by a decreased responsiveness to PTH, as measured with the PA system in these cells. A loss of PTH receptors could modulate PTH responses in osteoblasts, either in the local control of bone formation and resorption, or in pathological conditions such as humoral hypercalcaemia of malignancy.

Binding, Competitive↗
PubMed1991

Localization of parathyroid hormone-related protein in breast cancer metastases: increased incidence in bone compared with other sites.

Parathyroid hormone-related protein (PTHrP) has recently been identified in 60% of a series of primary breast cancers. The detection of a bone-resorbing factor in tumors with a propensity to metastasize to bone prompted study of PTHrP in breast cancer metastasis. PTHrP was localized by immunohistology in 12 of 13 (92%) breast cancer metastases in bone and in 3 of 18 (17%) metastases in non-bone sites. The statistical difference was highly significant (P less than 0.0001). Production of PTHrP as a bone-resorbing agent may contribute to the ability of breast cancers to grow as bone metastases.

Bone Neoplasms↗